The overall objective of this project is to improve our knowledge of respiratory control systems. Much progress has been made in the first 2 years of this project in determining the role of the peripheral chemoreceptors and cerebrospinal fluid (CSF) acid-base balance in ventilatory control at sea level and high altitude. The data strongly suggest that other central nervous system factors are important in control of respiration during acclimatization to chronic hypoxia. Our specific goals, then, for the coming year are to examine the role of the peripheral chemoreceptors and CSF acid-base balance in exercise at sea level and during acute and chronic hypoxia. Additional goals will be to begin examination of methods to study, by means of electrode implantation, respiratory activity in the neocortex and reticular formation in awake ponies. A system will also be developed for carrying out cerebral perfusion involving infusions of artificial CSF into the lateral ventricles and via the cisterna magna in awake animals. The perfusion system will be used to examine the roles of biogenic amines in respiratory control.